Reactions of trimethylsilyl-derived iodohydrins with electron-rich π-systems

Reactions of trimethylsilyl-derived iodohydrins of the type R¹R²CH–CH(I)OTMS, with electron-rich olefins, and the effects of certain factors on these reactions, were studied. The trimethylsilyl-derived iodohydrins were obtained in situ by reacting R¹R²CH–CHO (R¹ = R² = H; R¹ = H, R² = alkyl, phenyl) with TMSI. The corresponding trimethylsilyl enol ether derivatives (R¹R²C&═CH–OTMS), and 1,1-diarylethylenes were the olefins used. Aldehydes of the type RCH₂–CH&═O reacted smoothly in the presence of TMSI to yield the condensation product RCH₂–CH&═C(R)–CH&═O. Both RCH(–CH&═CAr₂)₂ and the cyclic acetal 5 were obtained as main products of the RCH&═O–TMSI–CH₂&═CAr₂ reaction system, depending on the [RCHO] ∶ [TMSI] ∶ [CH₂&═CAr₂] concentration ratio. The mechanisms of formation for the various main products and by-products are discussed. TMSI substitutes, formed by reacting Me₃SiCl with each of several Lewis acids, were also used.